THE PREPARATION OF CULTURE MEDIA 155 



and filtered through sterile gauze. One part of meat juice is added to two 

 parts of egg by volume. 



III. Gentian Violet. 1 per cent alcoholic solution of gentian voilet is 

 added to make a final proportion of 1 : 10,000. 



The three ingredients are well mixed. The medium is tubed and inspis- 

 sated as usual. 



Petroff recommends for sputum the following technique: Equal parts 

 of sputum and 3 per cent sodium hydroxid are shaken and incubated at 

 38 C. for 15 to 30 minutes, the time depending on the consistency of the 

 sputum. The mixture is neutralized to litmus with hydrochloric acid and 

 centrifugalized. The sediment is inoculated into the medium described above. 

 Pure cultures are obtained in a large proportion of cases. 



SYNTHETIC MEDIA FOR THE TUBERCLE BACILLUS. A considerable number 

 of synthetic media have been made for the growth of the tubercle bacillus. 

 The purpose of these media is to omit complex protein substances as much 

 as possible. The one- we give below is according to the formula used by 

 Petroff with success. 



0.35 gram K 2 HPO 4 



4.93 grams Mg HPO 4 . 2H 2 O 



10 c.c normal H 2 SO 4 



20 c.c normal (1/3 molar) H 3 PO 4 



10 c.c 3 times normal (molar) citric acid 



5.29 grams asparagin 



20 c.c glycerin 



1000 c.c water 



add 10 c.c. normal NaOH. 



Potato Media. Large potatoes are selected, washed in hot water, and 

 scrubbed with a brush. They are peeled, considerably more than the cuticle 

 being removed. The peeled potatoes are washed in running water, following 

 which cylindrical pieces are removed with a large apple corer. The cylinders 

 are cut into wedges. 



Since the reaction of the potato is normally acid, this should be corrected 

 by washing the pieces in running water over night, or, better, by immersing 

 them in a one per cent solution of sodium carbonate for half an hour. 



The pieces are then inserted into the large variety of test tubes known 

 as "potato tubes." (See Fig. 21, c.) In the bottom of the tubes a small 

 amount of water (about 1 c.c.) or a small quantity of moist absorbent cotton 

 should be placed in order to retard drying out of the potato. The tubes 

 are sterilized by fractional sterilization, twenty minutes to half an hour in 

 the Arnold sterilizer on three successive days. 



POTATO BROTH. Petroff has used extract of potatoes in fluid media for 

 the growth of tubercle bacilli. There are many different ways of preparing 

 the potato extract. The best way is to finely grind thoroughly, or grate the 



